#ifndef __TC_SHA256_H__
#define __TC_SHA256_H__

#include <stddef.h>
#include <stdint.h>

#ifdef __cplusplus
extern "C" {
#endif

#define TC_SHA256_BLOCK_SIZE (64)
#define TC_SHA256_DIGEST_SIZE (32)
#define TC_SHA256_STATE_BLOCKS (TC_SHA256_DIGEST_SIZE/4)

struct tc_sha256_state_struct {
	unsigned int iv[TC_SHA256_STATE_BLOCKS];
	uint64_t bits_hashed;
	uint8_t leftover[TC_SHA256_BLOCK_SIZE];
	size_t leftover_offset;
};

typedef struct tc_sha256_state_struct *TCSha256State_t;

/**
 *  @brief SHA256 initialization procedure
 *  Initializes s
 *  @return returns TC_CRYPTO_SUCCESS (1)
 *          returns TC_CRYPTO_FAIL (0) if s == NULL
 *  @param s Sha256 state struct
 */
int tc_sha256_init(TCSha256State_t s);

/**
 *  @brief SHA256 update procedure
 *  Hashes data_length bytes addressed by data into state s
 *  @return returns TC_CRYPTO_SUCCESS (1)
 *          returns TC_CRYPTO_FAIL (0) if:
 *                s == NULL,
 *                s->iv == NULL,
 *                data == NULL
 *  @note Assumes s has been initialized by tc_sha256_init
 *  @warning The state buffer 'leftover' is left in memory after processing
 *           If your application intends to have sensitive data in this
 *           buffer, remind to erase it after the data has been processed
 *  @param s Sha256 state struct
 *  @param data message to hash
 *  @param datalen length of message to hash
 */
int tc_sha256_update (TCSha256State_t s, const uint8_t *data, size_t datalen);

/**
 *  @brief SHA256 final procedure
 *  Inserts the completed hash computation into digest
 *  @return returns TC_CRYPTO_SUCCESS (1)
 *          returns TC_CRYPTO_FAIL (0) if:
 *                s == NULL,
 *                s->iv == NULL,
 *                digest == NULL
 *  @note Assumes: s has been initialized by tc_sha256_init
 *        digest points to at least TC_SHA256_DIGEST_SIZE bytes
 *  @warning The state buffer 'leftover' is left in memory after processing
 *           If your application intends to have sensitive data in this
 *           buffer, remind to erase it after the data has been processed
 *  @param digest unsigned eight bit integer
 *  @param Sha256 state struct
 */
int tc_sha256_final(uint8_t *digest, TCSha256State_t s);
/**
 * @brief Copy the the buffer 'from' to the buffer 'to'.
 * @return returns TC_CRYPTO_SUCCESS (1)
 *         returns TC_CRYPTO_FAIL (0) if:
 *                from_len > to_len.
 *
 * @param to OUT -- destination buffer
 * @param to_len IN -- length of destination buffer
 * @param from IN -- origin buffer
 * @param from_len IN -- length of origin buffer
 */
unsigned int _copy(uint8_t *to, unsigned int to_len, const uint8_t *from, unsigned int from_len);

/**
 * @brief Set the value 'val' into the buffer 'to', 'len' times.
 *
 * @param to OUT -- destination buffer
 * @param val IN -- value to be set in 'to'
 * @param len IN -- number of times the value will be copied
 */
void _set(void *to, uint8_t val, unsigned int len);

/*
 * @brief AES specific doubling function, which utilizes
 * the finite field used by AES.
 * @return Returns a^2
 *
 * @param a IN/OUT -- value to be doubled
 */
uint8_t _double_byte(uint8_t a);

/*
 * @brief Constant-time algorithm to compare if two sequences of bytes are equal
 * @return Returns 0 if equal, and non-zero otherwise
 *
 * @param a IN -- sequence of bytes a
 * @param b IN -- sequence of bytes b
 * @param size IN -- size of sequences a and b
 */
int _compare(const uint8_t *a, const uint8_t *b, size_t size);


struct tc_hmac_state_struct {
	/* the internal state required by h */
	struct tc_sha256_state_struct hash_state;
	/* HMAC key schedule */
	uint8_t key[2*TC_SHA256_BLOCK_SIZE];
};
typedef struct tc_hmac_state_struct *TCHmacState_t;

/**
 *  @brief HMAC set key procedure
 *  Configures ctx to use key
 *  @return returns TC_CRYPTO_SUCCESS (1)
 *          returns TC_CRYPTO_FAIL (0) if
 *                ctx == NULL or
 *                key == NULL or
 *                key_size == 0
 * @param ctx IN/OUT -- the struct tc_hmac_state_struct to initial
 * @param key IN -- the HMAC key to configure
 * @param key_size IN -- the HMAC key size
 */
int tc_hmac_set_key(TCHmacState_t ctx, const uint8_t *key, unsigned int key_size);
/**
 * @brief HMAC init procedure
 * Initializes ctx to begin the next HMAC operation
 * @return returns TC_CRYPTO_SUCCESS (1)
 *         returns TC_CRYPTO_FAIL (0) if: ctx == NULL or key == NULL
 * @param ctx IN/OUT -- struct tc_hmac_state_struct buffer to init
 */
int tc_hmac_init(TCHmacState_t ctx);
/**
 *  @brief HMAC update procedure
 *  Mixes data_length bytes addressed by data into state
 *  @return returns TC_CRYPTO_SUCCCESS (1)
 *          returns TC_CRYPTO_FAIL (0) if: ctx == NULL or key == NULL
 *  @note Assumes state has been initialized by tc_hmac_init
 *  @param ctx IN/OUT -- state of HMAC computation so far
 *  @param data IN -- data to incorporate into state
 *  @param data_length IN -- size of data in bytes
 */
int tc_hmac_update(TCHmacState_t ctx, const void *data, unsigned int data_length);
/**
 *  @brief HMAC final procedure
 *  Writes the HMAC tag into the tag buffer
 *  @return returns TC_CRYPTO_SUCCESS (1)
 *          returns TC_CRYPTO_FAIL (0) if:
 *                tag == NULL or
 *                ctx == NULL or
 *                key == NULL or
 *                taglen != TC_SHA256_DIGEST_SIZE
 *  @note ctx is erased before exiting. This should never be changed/removed.
 *  @note Assumes the tag bufer is at least sizeof(hmac_tag_size(state)) bytes
 *  state has been initialized by tc_hmac_init
 *  @param tag IN/OUT -- buffer to receive computed HMAC tag
 *  @param taglen IN -- size of tag in bytes
 *  @param ctx IN/OUT -- the HMAC state for computing tag
 */
int tc_hmac_final(uint8_t *tag, unsigned int taglen, TCHmacState_t ctx);

#ifdef __cplusplus
}
#endif

#endif /* __TC_SHA256_H__ */